One of the oldest commercial processes for dissolving gold is the so-called "cyanide process" which is illustrated by the following reaction: EQU 2Au + 1/2O.sub.2 + H.sub.2 O + 4CN.sup.- = 2Au (CN).sub.2 .sup.- + 2OH.sup.-
the cyanide ion forms such a stable complex with aurous gold that when the cyanide ion is present oxygen of the air is sufficient to oxidize gold. The effectiveness of the cyanide process has led to its commercial usage for both extraction of gold from its ores and for the reclamation of gold from gold coated scrap parts. Generally a potassium cyanide solution is used in the "cyanide process". This solution is very toxic and disposing of spent cyanide solution has become a significant and increasing waste disposal and pollution abatement control problem.
Gold has also been dissolved using a mixture of hydrochloric acid and nitric acid, known as "aqua regia", in order to obtain the complex chlorauric acid, HAuCl.sub.4. Aqua regia, however, is extremely corrosive and yields toxic fumes.
In order to avoid the use of very toxic chemicals and mitigate waste disposal and pollution abatment control problems attempts have been made to develop an economically viable process for the reclamation of gold. With the skyrocketing price of gold and industry's concern about ecology a new commercially feasible gold reclamation process has been sought which is relatively safe from a production viewpoint and which mitigates pollution abatement problems.
A new process has now been developed. While not limited solely to reclamation type operations, the new process is particularly effective in recovering gold from parts and devices used in the electronics industry including gold plated printed circuit boards and other gold coated metal, plastic, glass and ceramic parts. Such parts may contain between 2 and 100 micro inches of plated gold. The new process involves the use of a potassium iodide-iodine solution to dissolve the gold. While such a solution has been used to etch out thin film gold circuits in microelectronic devices and to strip plated gold for thickness measurements, potassium iodide-iodine solutions have heretofore been considered too expensive for consideration in any commercial operation for recovering gold.